1. Field of the Invention
The present invention relates to a control apparatus of a cylinder-inside injection-type internal-combustion engine, and in particular to a control apparatus of the internal-combustion engine in which, under its homogeneous-charge compression-ignition combustion-mode control, an ignition timing control is performed when a transient operating state occurs.
2. Description of the Related Art
In recent years, associated with variations or the like of atmospheric pollution and petroleum conditions, the enhancement in exhaust-gas quality and fuel consumption of an internal-combustion engine (hereinafter referred to as an “engine”) is strongly demanded. As one method among those to enhance exhaust-gas quality and fuel consumption of an engine using gasoline, a combustion control by homogeneous-charge compression ignition (hereinafter referred to as an “HCCI,” HCCI: Homogeneous-Charge Compression Ignition) receives attention in which the combustion in the gasoline engine is achieved by making a fuel-air mixture higher in temperature and in pressure at the latter part of a compression stroke and by self-igniting the fuel-air mixture, without using spark-discharge ignition.
In HCCI combustion, fuel consumption can be reduced by combustion with leaner fuel-air mixture in comparison with spark-discharge ignition combustion, and reduction of nitrogen oxides (NOx) can be achieved at lower combustion temperatures in comparison with spark-discharge ignition combustion; meanwhile, for example, at a fuel-air mixture temperature equivalent to that of spark-discharge ignition, the temperature is too low to advance self-ignition, causing in occurrence of a misfire; and, when the fuel-air mixture temperature is increased too far, a combustion speed becomes excessively high, causing in occurrence of knocking. To this end, it is well known in the art that, in order to obtain the fuel-air mixture temperature that advances the HCCI combustion better, a control technique employs an internal exhaust-gas recirculation (hereinafter referred to as an “internal EGR,” EGR: Exhaust Gas Recirculation) due to a negative valve overlap in which an exhaust valve is closed when a piston is before the top dead center of intake, and an intake valve is opened when the piston is after the top dead center of intake, so that the fuel-air mixture temperature is increased.
According to this art well known, there arises a case in which, in an operating area where the number of revolutions of the engine is relatively low and the load is relatively light, HCCI combustion can be achieved by employing the internal EGR so as to control the fuel-air mixture temperature inside of a cylinder; however, in an operating area where the number of revolutions of the engine is further lower and the load is further lighter, the fuel-air mixture temperature does not reach a level in which good HCCI combustion is performed, because the combustion temperature is too low even if the internal EGR is employed. To this end, as a control capable of obtaining good HCCI combustion even in those cases described above, an ignition assist control is conceivable which introduces spark-discharge ignition for enhancing self-ignition.
For example, in Japanese Patent Application Publication No. 2005-016408, an HCCI combustion control is made possible in which, in an HCCI combustion mode, an ignition assist is performed by spark-discharge ignition to a fuel-air mixture before the top dead center of compression using an ignition timing characteristic responding to an octane number being set in advance, so that a misfire or knocking does not occur.